The number of systems that involve multiple sensors or other data sources from which information streams combine together to produce a desired data product continues to increase. Examples include solid-state camera detector arrays, synthesis telescopes, networks of traffic sensors, location information from mobile phones, and antenna arrays. The data products may include simple integration, data compression, and data combinations in multiple dimensions according to arbitrary rules, and may also include local operations where the required product results from behavior of the nodes. In this last case, the nodes may receive messages or tasks from a central processing facility as well.
A particular subset of such systems does not have a single desired data product, but combines the data in multiple ways to provide multiple, distinct data products. Examples include distributed passive radar arrays and phased array radars, both of which need to track indeterminate and time-varying target populations, and networks of surveillance cameras that may need to track multiple disparate objects of interest like people and vehicles simultaneously.
Generally, transferring the data from all of the data providers to a central processing unit addresses all of the data assimilations. The central processing facility applies the appropriate algorithms to extract the desired data product. In the other direction, the central processing facility transfers messages to all of the data recipients to cause the desired behavior. In either case, the data transfer requirements will overwhelm the system, either between the nodes and the central processing facility, or within the processor or processors. The addition of additional processors may not alleviate the bandwidth requirements because the data still needs to traverse the connections to get to the processors and may result in transferring the bandwidth requirements to other, less tractable areas of the network.
One approach uses very high bandwidth, and therefore high cost, connections between the nodes and the central processor. For example, synthesis radio telescopes use high-bandwidth optical connections between the antennas and the processing facility, or ultra-fast communication links between processors in supercomputing installations.
Alternatively, wider bandwidth communications and/or multiple processors or networks may handle small numbers of data products, but these solutions rapidly become untenable, if not impossible, at any cost. For example, where the system requirement needs to track every potentially hostile target, any inability to add a new target to the track can be fatal.